In automated industrial systems, such as production lines, where for example industrial robots are used, components stored in a disordered bulk storage are required to be fed as individual components in order for various operations to be performed. There exist many feeding devices using different principles and which are suitable for different specific tasks. One type of feeder is a type in which randomly oriented components are fed onto and displayed on a picking surface. An image processing system is typically used in order to determine which components on the picking surface are correctly oriented in order to be pickable by the robot. These types of feeders are flexible since they are not limited to a certain type of component.
According to prior art, the image processing system makes use of a camera that is mounted directly overhead of the picking surface. The camera takes images of the components dispersed on the picking surface and these images are used in robot-vision software to direct a robot gripper to the components to be picked. From U.S. Pat. No. 4,876,728 is known a microprocessor based vision system that includes an overhead camera and two overhead light sources arranged over a conveyor belt, which system is interfaced with a robot system.
From WO2013/113535 is known a component feeder having a bulk storage container, inside which a lift is arranged. The lift has a lift platform that lifts components up from the container and disperses them onto a picking surface, located above the container. A vision system comprising an overhead camera is arranged over the picking surface, and an image is used to determine which components are correctly oriented to be pickable by a robot tool. The picking surface may be transparent and it may be provided with a backlight arrangement comprising a light source arranged underneath the transparent picking surface.
U.S. Pat. No. 6,002,125 discloses an optical device possessing light-sensitive COD-contact sensors for determining the position of components on a conveyor belt moving relative to the sensors. Light sources illuminating the conveyor belt are positioned along at least one scanning line and they lights across the direction of movement of the conveyor belt. The COD-contact sensors are arranged underneath the conveyor belt and the light source illuminates the conveyor belt from above. The contact sensors are mounted straight beneath at the underside of a fixedly mounted transparent glass plate, above which the conveyor belt slides across at the smallest possible pace. At least one row of light-sensitive sensors along the scanning line is set to register the light radiance generated by the items passing between the light source and the sensors. The sensors can be settled on the side of a transparent conveyor belt at a distance from the light source to register the shadow cast by the items passing.
A trend in automation is towards collaborative human-robot assembly. A number of new small robots designed specifically for this mode of working have been launched in recent years, but developments in the field of material handling to support these robots has been slow by comparison. Conveyor belts provide one solution, but in compact lines, a more common solution is hand-to-hand transfer of the objects. In this approach, parts and work pieces are placed by one operator into a designated output-buffer area from where they can be picked up by the operator at the neighboring station. While it is easy for a human to pick up randomly-placed components from the input buffer, a robot requires a vision system for this task.
Existing methods for locating components passed by a human operator to the material input buffer of a robot require the use of either an overhead vision system or a fixture. Both approaches involve extra set up effort and hardware outlays. If an overhead camera is used, then this must be calibrated and installed on a robust mounting to avoid position errors due to external disturbances. Further, images generated by a conventional camera suffers from perspective effects which produce further position-dependent distortions. Another disadvantage with an overhead camera is that some part of the robot arm may block the camera view or cast shadows when an image is taken.
External lighting may also be required depending on the application. Skill is also required in the programming of the vision job itself. Furthermore, when programming the movement cycle of the robot, great care must be taken to ensure that the robot neither blocks the view of the camera nor casts shadows from the lighting at the point in time when an image is taken. This complicates the task of programming the robot, impacts on cycle-time, and increases integration effort.
Alternatively, a camera can be mounted on the robot hand. If a hand-mounted camera is used to locate parts on the input buffer, then this will also incur a cycle-time penalty. The use of fixtures in order to avoid the need for a vision-system places extra demands on the human operator which can also impact overall cycle time. Furthermore, engineering effort is required to design and install the fixture, which both increases system cost and reduces flexibility. Using a fixture can also be a disadvantage as shape of the components to be picked may vary.
Skill is also required in the programming of the vision job itself. Furthermore, when programming the movement cycle of the robot, great care should be taken to ensure that the robot neither blocks the view of the camera nor casts shadows from the lighting at the point in time when a picture is taken. This complicates the task of programming the robot, impacts on cycle-time, and increases integration effort. If a hand-mounted camera is used to locate parts on the input buffer, then this will also incur a cycle-time penalty. The use of fixtures in order to avoid the need for a vision-system places extra demands on the human operator which can also impact overall cycle time. Moreover, engineering effort is required to design and install the fixture, which both increases system cost and reduces flexibility. Fixtures are non-adjustable devices and are thus not practical to use as the items on a component feeder can be various in shape and size. Finally, if a camera is installed on the robot itself, this also makes it slow to localize the components and accordingly the cycle time becomes slower.